In the production of crude oil and gas, it is frequently desirable to inject water into subsurface formations at an injection well. Water travels through the formation and displaces crude oil contained therein towards a production well.
Water injected into the subsurface formation is typically water that has been produced in association with crude oil in the vicinity of the injection well. The water is separated from the crude oil and pumped to a variety of injection wells from a central pumping location. In other cases, seawater is utilized. In a typical produced water injection system, the pumps produce pressures upwards of 4300 pounds per square inch (psi) or more.
Certain injection wells will accommodate the water injected therein more easily than others. This occurs for any one of a variety of reasons that include, for example, variations in the porosity of the subsurface formation. Water naturally flows preferentially into the wells which impose lesser resistance to flow. However, it is frequently desirable to direct larger quantities of water into wells which produce greater resistance to flow. Therefore, it is necessary to restrict the flow into many injection wells. This is commonly done with one of a variety of choke valves.
The most commonly used choke valve on water injection wells are those like the "Gray PBS Adjustable Choke" manufactured by Gray Tool Company. See also U.S. Pat. No. 4,444,220. This type of valve utilizes a vertically oriented hollow body member with an inlet oriented perpendicular to the body member. A tip assembly is raised and lowered within the body member to block or restrict fluid flow from the inlet. This type of valve has been found by the inventor to be subject to frequent failure for a number of reasons. First, the valves are designed such that the fast flow through the device is forced to turn a full 90.degree. at the inlet. The high pressure and fast fluid velocities result in wear to the tip, vibration, and, eventually, total detachment of the tip. This problem is particularly severe in choke valves used in water injection wells because (a) the water is prone to contain sediment and the like, aggravating wear on the tip and (b) extremely high pressure drops (on the order of 2000 psi or more) are often created, resulting in very high fluid velocities. Additional problems with this type of valve result from the use of packing material (to isolate the stem used to raise and lower the tip from the outside environment).
Further, these valves frequently have many parts, resulting in a complex system which is subject to failure. For example, a seat is screwed into the valve body and is used to contact the tip for the purpose of sealing. It has been found that the threads of this seal become loose (again, due to the extreme conditions to which the interior of the valve is subjected) and rapidly errode/corrode to the point where the seat becomes unserviceable or fails. This problem is particularly troublesome because the seat is difficult to access, resulting in high costs for repair/replacement. In general, any type of internal threaded connection in a choke valve will be prone to failure due to erosion and corrosion effects.
Valves have been proposed for the control of fluids in other applications. For example, U.S. Pat. No. 1,925,531 describes a valve in which a slidable piston 15 is installed in a cylindrical valve body A. The slidable piston controls the flow of fluids by sliding around radially mounted inlet ports 4 in a housing. It is apparent that fluid flowing through the valve would have a high velocity and change direction in or near ports or edges such as those in the inlet ports. Further, when the valve is throttled, the edges of the sliding sleeve would be subjected to severe erosion/corrosion effects. These combined effects would result in failure of the valve in a short period of time.
Other types of sliding sleeve valves have been proposed (e.g., U.S. Pat. No. 2,676,611). In all of these situations it is found that an exposed edge of the sleeves and/or another portion of the valve which is necessary for proper sealing is exposed to severe erosion/corrosion effects due to its exposed nature. Other disadvantages lie in the use of a complex apparatus which is prone to failure, and the use of screwed fittings inside the valve.
It is desirable, therefore, to provide a choke valve which is simple in construction, resulting in higher reliability and easy service. It is further desirable to provide a valve which requires no internal threaded connections. It is further desirable to provide a choke valve which minimizes the number of items a flowing fluid must change direction and which does not cause fluid to change direction at a port or exposed internal edge. It is still further desirable to provide a valve which does not require packing material to isolate fluid inside the valve.